Motion encoders can e.g. be used to find the speed of a conveyor belt, just to mention a straightforward and simple example. Normally a mechanical encoder connected to the conveyer motor would be used. However, if for some reason it is not allowed to have the encoder in physical contact, optical techniques based on sensing of light can be used instead. One solution is to use a Doppler laser, which is accurate but expensive. Another solution is to use a conventional camera, e.g. CCD based, and image processing, which is relatively less expensive but requires more processing and may still be a too costly option. Owing to the processing requirements, energy consumption may also be higher than what may be desirable, e.g. in case of a battery powered sensor. Hence, conventional solutions may make some application areas and use cases of no or less practical interest. Hence, relatively much processing is required for conventional optical motion encoders, and they are more costly and energy demanding than what may be desirable, at least in some situations.